Which organelle is the site of cellular respiration?

• A. Mitochondria
• B. Nucleus
• C. Chloroplast
• D. Golgi apparatus

Answer: (A)

Cellular respiration is the process by which cells convert the chemical energy in glucose into ATP, the energy currency they use. The mitochondria are where most of that energy production happens. In the mitochondrion, the citric acid cycle runs in the matrix, generating electron carriers, while the inner membrane hosts the electron transport chain. The flow of electrons through this chain creates a proton gradient that powers ATP synthase to produce most of the cell’s ATP. Glycolysis, which makes a smaller amount of ATP, occurs in the cytosol and feeds substrates into the mitochondrial pathways. The nucleus stores genetic material and does not generate ATP; chloroplasts perform photosynthesis in plant cells (not respiration); and the Golgi apparatus handles protein modification and shipping, not energy production.